This invention relates generally to imaging systems and more particularly to an imaging system that produces multiple images of a single object scene onto a single detector array. These multiple images are spatially displaced from one another on a single detector array in the image plane.
In some specialized applications, such as long-range multi-spectral imaging, there is a great desire to produce several images of a given object scene simultaneously on a single detector array (such as a CCD). For applications such as multi-spectral imaging, each of these separate images is passed through a different colored filter. Presently, multi-spectral imaging is typically performed either with rotating filter wheels (which are unable to record more than a single image simultaneously) or with a plurality of imaging and detection systems (which inherently are unable to image onto a single detector array).
Multi-spectral systems that rely on rotating filter wheels produce images through various filters, one-at-a-time, and in succession. In cases where it is important to produce differently-filtered images simultaneously, filter-wheel-dependent multi-spectral systems are inadequate.
U.S. Pat. No. 5,194,959 describes a multi-spectral imaging system that produces differently-filtered images simultaneously on three different imaging sensors. One major drawback with this system is that three imaging sensors, which can often be quite expensive, are required. In addition, in cases where high-performance and/or low-contrast imaging is to be performed, it is desirable to compare images formed on a single imaging sensor. The reason for this is that every imaging sensor, no matter how similar, is different in some way than every other imaging sensor. For example, something as simple as a slight difference in temperature stability between two imaging sensors can make very fine comparisons of images made on the two imaging sensors practically impossible. For many multi-spectral applications, it is absolutely necessary to produce multiple images on a single imaging sensor.
U.S. Pat. Nos. 4,933,751, 5,024,530, 5,642,191, 5,729,011, and 5,926,283 each describe an apparatus and/or method for producing multiple images simultaneously on a single imaging sensor. All of these prior art patents have shortcomings which are directly addressed in the invention described herein.
U.S. Pat. Nos. 4,933,751 and 5,926,283 describe apparatuses that require mirror reflection of the optical beam in so-called “off-axis” or “perpendicular” directions. Because of the convoluted orientation of the multiple off-axis mirrors in these designs, complex positioning systems are required., These patents also describe apparatuses that do not to minimize vignetting.
U.S. Pat. No. 5,729,011 describes an apparatus that positions both the image-separating prism and the filter array at a point in the optical train where the light is converging. Positioning of the prism at a point in the optical train where light is converging introduces a number of aberrations and degrades image quality. Furthermore, positioning of the filter array at a point in the optical train where light is converging necessarily causes light to be incident on the filters at a wide range of angles (corresponding to the angles at which the light is converging). It is well-known in the field of interference filters that filters' spectral transmission properties vary greatly with angle. Furthermore, this apparatus does not minimize vignetting.
U.S. Pat. No. 5,642,191 describes an apparatus that positions the filter at a point in the optical train where the light is converging. This presents the same shortfalls presented in the case where a filter array is placed in a converging beam. Furthermore, splitting of the image into only two images is anticipated, and means are not shown for the more complex case where four or more images are to be produced. Furthermore a system of two, concentrically located prisms is required, which is more complicated to align than a single prism would be.
U.S. Pat. No. 5,024,530 describes an apparatus that does not prevent light from each of the multiple images from spilling over into neighboring images. Furthermore, splitting of the image into only two images is anticipated, and means are not shown for the more complex case where four or more images are to be produced.
It is therefore an object of this invention to produce multiple images of the same object scene simultaneously and adjoining one another on a single detector plane.
It is another object of this invention to effect such imaging with an optical system that exhibits no vignetting.
It is another object of this invention to effect such imaging with an optical system that requires no off-axis optical elements.
It is another object of this invention to effect such imaging with an optical splitting means that comprises a single refractive prism.
It is another object of this invention to effect such imaging without the use of mirrors.
It is another object of this invention to effect such imaging with an optical system that allows adjustment of the size of each image constituting the multiple images.
It is another object of this invention to effect such imaging with an optical system that allows adjustment of orientation and placement of the multiple images.